1. Field of the Invention
The present invention relates generally to a vane-type rotary compressor, applicable for such as an automotive air conditioner system. More specifically, the invention relates to a light weight vane-type rotary compressor which is free from influence of heat.
2. Description of the Background Art
Japanese Patent First (unexamined) Publication (Tokkai) Showa 61-89991 discloses a light weight vane-type rotary compressor. In order to reduce the weight of the assembly, the principle components, i.e. cam ring, rotor and an inlet-side side plate are formed of aluminium-type metal. A compressor mechanism comprising the rotor, vane, can ring and so forth, is housed within a cover shell in order to suppress variation of substantially small clearance between the cam ring and the rotor. Namely, as is well known, the cam ring defines an essentially oval or elliptic rotor receptacle opening in order to house the rotor which carries a plurality of rotor vanes. The rotor is supported by a rotor shaft which is driven by a drive, such as an automotive internal combustion engine and disposed in the rotor receptacle opening of the cam ring to define a substantially small clearance at the smallest diameter section. The rotor vanes are received within radial grooves formed in the rotor and moves toward and away from the inner periphery of the rotor receptacle opening to establish fluid tight seal and thus to define pressure chambers. The rotor is cooperative with the the inner periphery of the rotor receptacle opening for varying the volume of the pressure chamber over each cycle of rotor revolution to repeat compressor cycles which includes strokes of induction, compression and discharge.
With such construction, because the aluminium type metal has relatively large thermal expansion coefficient, the clearance can vary due to temperature difference between the rotor and cam ring. Namely, compressing the fluid in the compression stroke, heat is generated which raises the temperature of the cam ring and the rotor. When the cam ring is exposed to the atmosphere, the heat transferred to the cam ring is radiated. On the other hand, since the rotor is enclosed in the rotor receptacle opening in the cam ring, it may cause thermal expansion much greater than that caused in the cam ring.
In the above-identified prior publication, the cam ring and rotor are formed of a the aluminium type metal or metals having substantially the same linear expansion coefficient. The assembly of the compressor mechanism is enclosed in the shell cover so as to reduce radiation of the heat from the cam ring so as to minimize temperature difference between the cam ring and the rotor. With such construction, the shell cover may cause increasing weight which is against the task for reduction of the weight of the unit. Furthermore, the shell cover may incur additional cost to cause rising of the production cost. However, the shell cover is regarded as inevitable component because exposure of the cam ring to the atmosphere may cause substantial temperature difference between the can ring and the rotor, which temperature difference may cause contact between the outer periphery of the rotor and the inner periphery of the rotor receptacle opening of the cam ring. This may cause burning on of the rotor onto the cam ring.